Vegetarian Nutrition

VN: Micronutrients in Pregnancy (2007)

Citation:
King JC, Stein T, Doyle M. Effect of vegetarianism on the zinc status of pregnant women. AJCN 1981 34: 1049-1055. PubMed ID: 7234736
 
Study Design:
Cross-Sectional Study
Class:
D - Click here for explanation of classification scheme.
Quality Rating:
Neutral NEUTRAL: See Quality Criteria Checklist below.
Research Purpose:
Compare the zinc status, as measured by plasma, urinary, and hair zinc levels, of a group of pregnant vegetarians in their last trimester with a group of pregnant nonvegetarian and a group of nonpregnant vegetarians.
Inclusion Criteria:
  • Last trimester of pregnancy
  • Non-smoker
  • Not currently taking oral contraceptives (nonpregnant women)
Exclusion Criteria:

Failure to complete 3 day food intake record

Description of Study Protocol:

Design

  • Subjects scheduled for interview during third trimester of pregnancy.
  • Blood, urine, and hair samples were collected for zinc analysis after interview.
  • Three day food records (2 weekdays, one weekend) were recorded after interview by subjects and returned via mail. 

Nutritional intervention: Subjects were provided with informal nutritional counseling during the interviews. Also, based on analysis of the subjects' three-day food record, subjects were provided with suggestions for improving the quality of their diets.

Statistical Analysis

Analysis of variance.  The Dunn multiple comparison test was used to evaluate significant differences between groups.  Nonrepeating variables were cross-tabulated and chi-squared determination wer made.

 

Data Collection Summary:

Timing of Measurements

 Third trimester of pregnancy

Dependent Variables

  • Zinc status as measured by plasma, urinary, and hair zinc levels

Independent Variables

  • Type of diet: vegetarian versus non-vegetarian
Description of Actual Data Sample:

Initial N: 23 (12 vegetarian pregnant women, 6 pregnant nonvegetarian women, 5 vegetarian nonpregnant women)

Attrition (final N): 20

Age: 22-31 (nonpregnant women were 3-5 years younger than the pregnant women)

Anthropometrics:

  • Prepregnancy weight of vegetarian group (kilograms): 60±9
  • Prepregnancy weight of nonvegetarian group (kilograms): 62±12
  • Nonpregnant vegetarian group weight (kilograms): 51±4

Location: California

Summary of Results:

 Zinc Intake

 

Pregnant Vegetarian

(n=9)

Pregnant Nonvegetarian

(n=6)

Nonpregnant Vegetarians

(n=5)

Statistical Significance Between Pregnant and Nonpregnant Groups

Statistical Signficance Within Groups

Zinc (mg)

12.6±0.9

14.4±0.6

6.4±0.8

p< 0.005

p<0.001

  Zinc Intake per 1000 Calories

 

Pregnant Vegetarian

(n=9)

Pregnant Nonvegetarian

(n=6)

RDA for Pregnant Women

Nonpregnant Vegetarians

(n=5)

RDA for Nonpregnant Women

Zinc (mg)

5.15

7.19

8.7

4.8

7.1

In all three groups, zinc intake per 1000 calories was less than the standard.  Fifty three percent of the pregnant women and 80% of the nonpregnant women selected diets which provided less than two-thirds of the RDA of zinc.

Diet, Plasma, Urinary, and Hair Zinc Levels

 

Diet (mg/day)

(mean±SEM)

Plasma** (µg/100g)

(mean±SEM)

Urine (mg/g of creatinine)

(mean±SEM)

 Hair (µg/g)

(mean±SEM)

 

Pregnant Vegetarians

12.4±1.3

(29.6±10.9)*

60±3

0.39±0.07

 177±7

 

Pregnant Nonvegetarians

 14.4±0.5

(16.1±1.8)*

 66±2

 0.41±0.06

 178±6

 
Nonpregnant Vegetarians

6.4±1.3

80±4

0.17±0.04

179±12

 

*Mean±SEM of diet plus supplemental zinc.

**Difference between groups significant (p<0.01).

Even though the nonpregnant women consumed significantly less zinc than the pregnant women (p<0.05), the plasma zinc levels of the nonpregnant women were significantly higher than the pregnant women (p<0.01).  Plasma zinc was about 21% lower in the pregnant women than the nonpregnant women.  The average urinary zinc concentration per gram of creatinine was about twice as high in the two pregnant groups than in the nonpregnant group (difference not significnat).  The hair zinc concentration was essentially the same in all three groups.

Use of supplemental zinc did not appear to have any effect on plasma, urinary, or hair zinc levels in the two pregnant groups.

Author Conclusion:
Consumption of an ovo-lacto vegetarian diet did not appear to alter zinc status in this group of pregnant women studied.  Plasma zinc levels may be reduced by upwards of 25% in women during pregnancy.  Urinary zinc may be elevated in pregnant women due to the increased glomerular filtration rate, or to a reduction in tubular reabsorption, or to an increase in the excretion of amino acids which bind zinc. 
Funding Source:
Government: NIH
Reviewer Comments:

Weaknesses:

  • Investigators failed to provide any information on ethnicity of subjects or information on recruitment of subjects.
  • Nutrition intervention (informal counseling and diet recommendations based on 3 day diet record) may have contaminated intake values.
  • Very small N. Number of subjects in comparison groups provides very little confidence.
Quality Criteria Checklist: Primary Research
Relevance Questions
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) N/A
  1. Would implementing the studied intervention or procedure (if found successful) result in improved outcomes for the patients/clients/population group? (Not Applicable for some epidemiological studies) N/A
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  2. Did the authors study an outcome (dependent variable) or topic that the patients/clients/population group would care about? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  3. Is the focus of the intervention or procedure (independent variable) or topic of study a common issue of concern to dieteticspractice? Yes
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) N/A
  4. Is the intervention or procedure feasible? (NA for some epidemiological studies) N/A
 
Validity Questions
  1. Was the research question clearly stated? Yes
1. Was the research question clearly stated? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.1. Was (were) the specific intervention(s) or procedure(s) [independent variable(s)] identified? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.2. Was (were) the outcome(s) [dependent variable(s)] clearly indicated? Yes
  1.3. Were the target population and setting specified? No
  1.3. Were the target population and setting specified? No
  2. Was the selection of study subjects/patients free from bias? No
2. Was the selection of study subjects/patients free from bias? No
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.1. Were inclusion/exclusion criteria specified (e.g., risk, point in disease progression, diagnostic or prognosis criteria), and with sufficient detail and without omitting criteria critical to the study? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.2. Were criteria applied equally to all study groups? Yes
  2.3. Were health, demographics, and other characteristics of subjects described? No
  2.3. Were health, demographics, and other characteristics of subjects described? No
  2.4. Were the subjects/patients a representative sample of the relevant population? No
  2.4. Were the subjects/patients a representative sample of the relevant population? No
  3. Were study groups comparable? No
3. Were study groups comparable? No
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) No
  3.1. Was the method of assigning subjects/patients to groups described and unbiased? (Method of randomization identified if RCT) No
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? No
  3.2. Were distribution of disease status, prognostic factors, and other factors (e.g., demographics) similar across study groups at baseline? No
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) Yes
  3.3. Were concurrent controls or comparisons used? (Concurrent preferred over historical control or comparison groups.) Yes
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? No
  3.4. If cohort study or cross-sectional study, were groups comparable on important confounding factors and/or were preexisting differences accounted for by using appropriate adjustments in statistical analysis? No
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.5. If case control study, were potential confounding factors comparable for cases and controls? (If case series or trial with subjects serving as own control, this criterion is not applicable.) N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
  3.6. If diagnostic test, was there an independent blind comparison with an appropriate reference standard (e.g., "gold standard")? N/A
  4. Was method of handling withdrawals described? Yes
4. Was method of handling withdrawals described? Yes
  4.1. Were follow-up methods described and the same for all groups? Yes
  4.1. Were follow-up methods described and the same for all groups? Yes
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) No
  4.2. Was the number, characteristics of withdrawals (i.e., dropouts, lost to follow up, attrition rate) and/or response rate (cross-sectional studies) described for each group? (Follow up goal for a strong study is 80%.) No
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.3. Were all enrolled subjects/patients (in the original sample) accounted for? Yes
  4.4. Were reasons for withdrawals similar across groups? No
  4.4. Were reasons for withdrawals similar across groups? No
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
  4.5. If diagnostic test, was decision to perform reference test not dependent on results of test under study? N/A
  5. Was blinding used to prevent introduction of bias? No
5. Was blinding used to prevent introduction of bias? No
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  5.1. In intervention study, were subjects, clinicians/practitioners, and investigators blinded to treatment group, as appropriate? N/A
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) No
  5.2. Were data collectors blinded for outcomes assessment? (If outcome is measured using an objective test, such as a lab value, this criterion is assumed to be met.) No
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? No
  5.3. In cohort study or cross-sectional study, were measurements of outcomes and risk factors blinded? No
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.4. In case control study, was case definition explicit and case ascertainment not influenced by exposure status? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
  5.5. In diagnostic study, were test results blinded to patient history and other test results? N/A
  6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
6. Were intervention/therapeutic regimens/exposure factor or procedure and any comparison(s) described in detail? Were interveningfactors described? Yes
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? N/A
  6.1. In RCT or other intervention trial, were protocols described for all regimens studied? N/A
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  6.2. In observational study, were interventions, study settings, and clinicians/provider described? Yes
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.3. Was the intensity and duration of the intervention or exposure factor sufficient to produce a meaningful effect? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.4. Was the amount of exposure and, if relevant, subject/patient compliance measured? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? Yes
  6.5. Were co-interventions (e.g., ancillary treatments, other therapies) described? Yes
  6.6. Were extra or unplanned treatments described? N/A
  6.6. Were extra or unplanned treatments described? N/A
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? Yes
  6.7. Was the information for 6.4, 6.5, and 6.6 assessed the same way for all groups? Yes
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
  6.8. In diagnostic study, were details of test administration and replication sufficient? N/A
  7. Were outcomes clearly defined and the measurements valid and reliable? Yes
7. Were outcomes clearly defined and the measurements valid and reliable? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.1. Were primary and secondary endpoints described and relevant to the question? Yes
  7.2. Were nutrition measures appropriate to question and outcomes of concern? No
  7.2. Were nutrition measures appropriate to question and outcomes of concern? No
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.3. Was the period of follow-up long enough for important outcome(s) to occur? Yes
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? No
  7.4. Were the observations and measurements based on standard, valid, and reliable data collection instruments/tests/procedures? No
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.5. Was the measurement of effect at an appropriate level of precision? Yes
  7.6. Were other factors accounted for (measured) that could affect outcomes? No
  7.6. Were other factors accounted for (measured) that could affect outcomes? No
  7.7. Were the measurements conducted consistently across groups? Yes
  7.7. Were the measurements conducted consistently across groups? Yes
  8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
8. Was the statistical analysis appropriate for the study design and type of outcome indicators? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.1. Were statistical analyses adequately described and the results reported appropriately? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.2. Were correct statistical tests used and assumptions of test not violated? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.3. Were statistics reported with levels of significance and/or confidence intervals? Yes
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? N/A
  8.4. Was "intent to treat" analysis of outcomes done (and as appropriate, was there an analysis of outcomes for those maximally exposed or a dose-response analysis)? N/A
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? Yes
  8.5. Were adequate adjustments made for effects of confounding factors that might have affected the outcomes (e.g., multivariate analyses)? Yes
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.6. Was clinical significance as well as statistical significance reported? Yes
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
  8.7. If negative findings, was a power calculation reported to address type 2 error? N/A
  9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
9. Are conclusions supported by results with biases and limitations taken into consideration? Yes
  9.1. Is there a discussion of findings? Yes
  9.1. Is there a discussion of findings? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
  9.2. Are biases and study limitations identified and discussed? Yes
  10. Is bias due to study's funding or sponsorship unlikely? Yes
10. Is bias due to study's funding or sponsorship unlikely? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.1. Were sources of funding and investigators' affiliations described? Yes
  10.2. Was the study free from apparent conflict of interest? Yes
  10.2. Was the study free from apparent conflict of interest? Yes